The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint.
In some cases, when a patient having a collapsed disc moves in extension (e.g., leans backward), the posterior portion of the annulus fibrosis or folding of the ligamentum flavum may further compress and extend into the spinal canal. This condition, called “spinal stenosis”, narrows the spinal canal and causes impingement of tissue upon the spinal cord, thereby producing pain.
There have been numerous attempts to provide relief for these afflictions by providing a spacer that inserts between adjacent spinous processes present in the posterior portion of the spinal column. This spacer essentially lifts the upper spinous process off of the lower spinous process, thereby relieving stenosis. In general, these interspinous implants are adapted to allow flexion movement in the patient, but resist or limit extension.
U.S. Pat. No. 6,068,630 (“Zuchermann”) discloses a spinal distraction implant that alleviates pain associated with spinal stenosis by expanding the volume in the spinal canal or neural foramen. Zuchermann discloses a plurality of implants having a body portion and lateral wings. The body portion is adapted to seat between the adjacent spinous processes, while the wings are adapted to prevent lateral movement of the body portion, thereby holding it in place between the adjacent spinous processes. The designs disclosed in FIGS. 15, 80 and 84 of Zuchermann comprise central body having an integral wing. Although the Zuchermann device achieves spinal distraction, it nonetheless possesses some limitations. First, since the Zuchermann central bodies have at least one integral wing, the clinician may encounter difficulty in sizing the central body independently of delivering the lateral wings. Second, the expansive geometry of the disclosed devices may not lend itself to minimally invasive surgical techniques seeking to conserve muscle mass and soft tissue in the regions adjacent the spinous processes.
U.S. Pat. No. 7,029,472 (Fortin) discloses a distraction device enabling management of the evolving deformation of the trunk of a child during growth. The device is easy to implant on account of its compact shape and includes two rods which can be bent and deformed on the ends thereof and which are mounted on a central adjusting member which is provided with a small hole for engaging a small tool that is designed to adjust the distance separating the elements for attachment to the bone. The inventive device can be locked in a position which is determined by the tightening of two screws which are disposed on the adjusting device.
U.S. Pat. No. 5,989,251 (Nichols) discloses an apparatus is disclosed for connecting first and second elongated spaced apart spinal rods to one another which includes a first connector having structure to engage a first spinal rod at a location along the length thereof and an elongated beam having an axis extending in a direction transverse to the first spinal rod, a second connector having structure to engage a second spinal rod at a location adjacent the first connector and including a reception portion projecting in a direction transverse to the second spinal rod and defining a channel for receiving the elongated beam of the first connector, and a locking member dimensioned and configured to engage the channel along the axis of the beam and secure the position of the beam with respect thereto.
U.S. Pat. No. 6,589,243 (Viart) discloses a posterior spinal osteosynthesis device for providing a transverse connection between two vertebral rods extending along a spinal segment wherein the device includes pairs of hooks adapted to laterally engage the vertebra with each pair being connected by a pair of parallel rods which are elastically bent to form a transverse arc whose ends are engaged in bores within the hooks.